1. Field of the Invention
The present invention relates generally to manufacture of semiconductor devices, and more particularly to a method of forming a metal film by CVD using a metal carbonyl material.
2. Description of the Related Art
Conventionally, chemical vapor deposition (CVD), which is a basic manufacturing process of semiconductor devices and allows film formation with good coverage even on a complicated structure having a high aspect ratio, is widely used for deposition of insulating films, semiconductor films, or metal films in the process of manufacturing semiconductor devices and display units such as liquid crystal display units.
In particular, the thermal CVD technology of metal films using a metal carbonyl material, which enables a film of refractory metal such as W to be formed with low resistance and, in addition, directly also on insulating films such as a SiO2 film, is important in multilayer interconnection structure technologies (see, for instance, Patent Document 1 and Patent Document 2).
Conventionally, deposition of a W film by thermal CVD is performed using a material such as WF6 or WCl6 and reducing this using H2, SiH4, or NH3. However, these methods have a problem in that it is difficult to deposit a W film on insulating films such as a SiO2 film.
On the other hand, the technique of forming a W film on a SiO2 film, using, for instance, W(CO)6 as a gaseous phase material, by a thermal decomposition reaction W(CO)6→W+6CO is proposed.
Such W film deposition by CVD using W(CO)6 as a material is typically performed in a temperature area of approximately 500° C. under pressures at or below approximately 7 Pa (0.5 Torr). Under these conditions, deposition of a W film occurs immediately on a SiO2 film with the start of the processing, and it is possible to form a high-quality W film with efficiency, that is, with high throughput. Here, the start of the processing is a timing at which supply of the gaseous phase material starts onto a substrate.
[Patent Document 1] Japanese Laid-Open Patent Application No. 10-135452
[Patent Document 2] Japanese Laid-Open Patent Application No. 2002-124488
FIG. 1 shows the relationship between deposition time and the film thickness of a formed W film, which was found by the inventors of the present invention when W film deposition was performed at low substrate temperatures at or below 500° C. using W(CO)6 as a gaseous phase material in experimental studies that form the basis of the present invention. In the experiment of FIG. 1, W film deposition was performed at a substrate temperature of 413° C. under a pressure of approximately 8 Pa (0.06 Torr) by supplying W(CO)6, with Ar gas bubbling of a flow rate of 50 SCCM, from a material container maintained at 25° C. to a reaction container (processing container). Here, the deposition time refers to a processing time that elapses from a timing at which supply of the gaseous phase material starts onto a substrate.
Referring to FIG. 1, it is found that deposition of a W film on a substrate does not occur immediately after the start of processing, and that it starts only after the passage of an incubation time of approximately 300 seconds, that is, approximately 5 minutes. After the passage of the incubation time, the film thickness of a W film increases linearly with deposition time.
The relationship of FIG. 1 shows that it is possible to form a W film on a SiO2 film with good accuracy even at such a low temperature by controlling deposition time. However, the existence of such incubation time at the start of processing reduces the throughput of a W film formation process. In particular, in a single-wafer film formation process that processes large-diameter substrates one by one, a wait time corresponding to the incubation time is generated for each substrate, thus causing a serious decrease in throughput in the entire manufacturing process of semiconductor devices. This incubation time further increases as the substrate temperature at the time of deposition is further reduced, and may reach 600 seconds or more. For instance, in the case of forming a W film by thermal decomposition of W(CO)6, setting the bubbler temperature at 30° C. and the flow rate of a gaseous phase material including W(CO)6 at 50 SCCM at a substrate temperature of 338° C. under 0.1 Torr, it has been found by the inventors of the present invention that an incubation time of 618 seconds, that is, more than 10 minutes, is generated although the deposition rate itself realizes a desired value of approximately 6.6 nm per minute.